1. Epizootiology of Myxobolus cerebralis, the Causative Agent of Salmonid Whirling Disease in the Rock Creek Drainage of West-Central Montana:
Willard O. Granath, Jr., Division of Biological Sciences, The University of Montana-Missoula and E. Richard Vincent, Montana Department of Fish, Wildlife and Parks, Bozeman, MT

2. Life Cycle of Myxobolus cerebralis
Fish dies and
myxospores
are released
Parasites migrate
through CNS to
associated cartilage
Myxospores in cartilage of infected fish
Life Cycle of
Myxobolus cerebralis
TAMS attach to the skin
of susceptible fish and sporoplasms penetrate
Myxospores are ingested
by T. tubifex
Development and
reproduction in
intestinal mucosa
TAMS released
days later
Polar filaments extruded 1

3. Myxospores of M. cerebralis

4. Clinical Signs of Whirling Disease

5. Susceptible Species of Salmonids
Coho salmon
Bull trout
Atlantic salmon
Brown trout
Rainbow trout
Golden trout
Brook trout
Danube salmon
Sockeye salmon
Cutthroat trout
Chinook salmon
Pink salmon

6. Scanning Electron Micrograph of T. tubifex

7. Ball of T. tubifex!!

8. Triactinomyxons of M. cerebralis

9. Background
1997- Initial sentinel fish studies by MFWP indicated that M. cerebralis was present in Rock Creek, a blue ribbon trout stream, located 37 Km east of Missoula, Montana.
Rock Creek was chosen as the site for a long- term, collaborative study, which is attempting to identify parameters affecting the transmission of M. cerebralis within this system.

10. N 50 Miles Blackfoot River Missoula Clark Fork River Rock Creek
Bitterroot River
Clark Fork River
Rock Creek
Hamilton
Missoula
Blackfoot River N
50 Miles

14. Field Studies
Sentinel cages are used to monitor M. cerebralis infections in trout at various sites throughout Rock Creek.
Oligochaete samples are taken at each site to examine:
the overall diversity and abundance of oligochaetes
the genetic heterogeneity of T. tubifex
the percentage of T. tubifex that are infected with M. cerebralis
Physical parameters are measured (water temperature, DO, pH, TDS; stream flow); EPA habitat assessment forms are filled out.
Nine sites were sampled in 1998, 1999, 20 sites in 2000, 21 sites in 2001, 22 sites in 2002, 2003, 2004, and 13 sites in 2005, 2006, 2007, 2008.

15. Sample locations in the Rock Creek Drainage
 8 Miles
Stony Cr.
East Fork
Middle Fork
Ross Fork
West Fork
Upper Willow Cr.
Hogback Cr. 4 5 3 7 6 8 9 11 10 12 13
14 -16 18 19 20 23 2 24 22 1 25 17 21
1 Upper Middle Fork
2 Lower Middle Fork
3 Upper East Fork (at bridge)
4 Lower East Fork (Upper Forks Bridge)
5 Ross Fork
6 West Fork
7 Forks Bridge
8 Watson’s Bridge
9 Bohrnsen’s Bridge
10 Gillie’s Bridge
11 Upper Willow Creek
12 Stony Creek
13 Windlass Bridge
14 Upper Puyear Ranch
15 Middle Puyear Ranch
16 Lower Puyear Ranch
17 Hogback Creek
18 Camp Siria)
19 Fish & Game
20 Valley of the Moon
22 Ranch Creek
23 Middle East Fork (Beaver Dam)
24 Clark’s Property
25 Mouth of Hogback Creek

17. “MacConnell-Baldwin Scale” Scoring Histological Lesions2 1 5 3 4
Grades 0-5
0 = no infection
1 = minimal
2 = mild
3 = moderate
4 = moderately severe
5 = severe

19. Average Grade of M. cerebralis Infections in Sentinel Rainbow Trout19

20. Average Grade of M. cerebralis Infections in Sentinel Rainbow Trout20

21. Prevalence of M. cerebralis Infection in Tubifex tubifex21

22. Habitat Assessments of Sample Locations
 8 Miles
Stony Cr.
East Fork
Middle Fork
Ross Fork
West Fork
Upper Willow Cr.
Hogback Cr.
185
102
178
128
186
184
154
148
182
155 – 200 = Optimal
115 – 154 = Sub-optimal
70 – 114 = Marginal
 70 = Poor
Barbour, M.T., J. Gerritsen, B.D. Snyder and J.B. Stribling, Revision to rapid bioassessment protocols for use in rivers and streams. EPA 841-D US EPA, Office of Water, Washington, DC.

23. BUT WHAT IS IT DOING TO THE FISH POPULATION?

24. Catchable Rainbow and Brown Trout Density Estimates in the Hogback Section (data from MFWP)

25. Summary of Field Studies
Disease severity in trout:
Low (<1.0)
High (>3.0)
Declining (<3.0)
No significant change in prevalence of infection of T. tubifex, but…
No dramatic change in water temperature; role of stream flow remains unclear.
Highest severity associated with presence of infected T. tubifex; but fish infected where no T. tubifex occur.
Higher worm abundance in degraded habitats.
Wild rainbow trout population has declined since 1993, but it appears to be rebounding.

26. Acknowledgments
National Partnership on Management of Wild and Native Cold Water Fisheries
Former UM graduate students: Mike Gilbert & JoMay Wyatt
Montana Department of Fish, Wildlife and Parks: Eric Reiland, Jody Hupka & Pat Saffel
The many landowners and concerned citizens in the Rock Creek drainage

27. Average Daily Water Temperature at Sentinel Cage Sites27

28. Average Daily Flow (cfs)
Average Daily Stream Flow for Rock Creek (USGS site # ) During Exposure Periods for
Average Daily Flow (cfs)